The hospitals have failed to meet A&E targets 18 times in the last 12 weeks.

One Lanarkshire GP said: “The health board sent out three letters indicating hospitals are not coping with acute admissions. This is before the winter deepens and bad weather prevails.

“We doctors are worried.”

Doctors are also angered by the suggestion that they would send patients to hospital who did not need to be there.

Labour MSP Richard Simpson, a former GP, said last night: “I am outraged that they would treat GPs in this way.

“Never in my life have I sent a patient for admission when I didn’t think they needed to be admitted.

“To tell GPs not to send patients into hospital is shocking. NHS Lanarkshire have already reduced the number of out of hours GP centres from five to two because they couldn’t staff them all.”

Associate medical director in primary care Chris Mackintosh, who signed one of the letters, said: “We appreciate that GPs are already aware of the referral processes but this important information is to give an up-to-date picture and to allow GPs to keep their patients informed.”

An NHS Lanarkshire spokesman said: “The centre coordinates all emergency referrals from GPs and links with the Scottish Ambulance Service to ensure patients get to the right service and the right hospital as quickly and efficiently as possible.”